1. The Field of The Invention
This invention relates to actuator apparatus and methods. More particularly, this invention relates to novel micropositioner systems and methods for controlling the position and movement of an object in one or more degrees of freedom using the forces generated by electric fields.
2. The Prior Art
There is a virtually limitless number of automated apparatus in use today. Such apparatus include items as varied as construction machinery, automobiles, kitchen appliances, and wrist watches. In all of these apparatus, some type of actuator is essential.
Generally speaking, an actuator is any apparatus which is capable of causing an object to move or to otherwise change its position. A wide variety of different types of actuators are currently in use.
For example, one of the most common types of actuators is an electric motor. An electric motor may, for example, be mechanically connected by means of gears, rods, or other structures to an object whose position and/or movement one desires to control. Then, by appropriately controlling the operation of the electric motor, the object can be moved and positioned in the desired manner.
A type of electric motor which has found wide use in the field of robotics is the electric stepper motor. An electric stepper motor is a motor which is designed to move and/or rotate an object a predetermined amount whenever an electric pulse is received by the motor. Thus, after appropriately coupling the stepper motor to the object one desires to move, movement of the object can be both controlled and monitored by controlling and monitoring the number of electric pulses which are transmitted to the stepper motor.
Conventionally pneumatic and hydraulic actuators are also widely used. Such actuators typically comprise two or more telescoping cylinders. Extension and retraction of the cylinders with respect to one another is controlled by pumping air or hydraulic fluid either into or out of a reservoir adjacent the cylinders.
A pneumatic or hydraulic actuator may, for example, be connected to an arm or beam. Movement of the arm or beam can then be controlled by appropriately extending or retracting the telescoping cylinders of the actuator.
While conventional actuators such as those described above are suitable for many applications, the performance of such actuators is, in many instances, unacceptable. For example, the conventional actuators often move with an abrupt or halting action and are generally limited to movement in only one linear or rotary degree of freedom. Moreover, the use of such actuators to obtain precise movement (of order micron scale) over short distances can be extremely difficult. Such precision of movement often requires the simultaneous use of numerous actuators of different sizes and types and/or the use of complex gearing or mechanical coupling arrangements.
In addition, conventional actuators are typically quite large and bulky. Such actuators can often be several times heavier than the objects they are being used to move. The weight and size of these actuators is, thus, a significant disadvantage in those applications in which space is extremely limited or where the object being moved is very small.
Recognizing the above-outlined drawbacks of conventional actuators, those skilled in the art have made various attempts to improve the performance characteristics of such actuators. Most of these attempts have been focused at providing the actuators with improved controllers. Those skilled in the art have generally postulated that desirable performance characteristics can be approached if care is used both in selecting and designing an appropriate actuator controller and in selecting the specific electric, pneumatic and hydraulic components of the actuator.
The results of such efforts to improve actuator performance have, however, been disappointing. While some performance improvement has been achieved, the improved actuator and controller are often even larger in size and weight. The improved actuator and controller are also often extremely expensive, complex, and difficult to manufacture.
Perhaps more significantly, the performance of the improved actuators remains largely unacceptable. Such actuators are still generally limited to moving an object in only one or two degrees of freedom, and the movement caused by such actuators is often still visibly mechanical.
Recently, a number of actuator devices have been developed which use electric and/or magnetic fields to directly control the position and movement of an object. Such actuator devices have, for example, been used in various types of accelerometers and gyroscopes.
For example, one such accelerometer includes a charged sphere. The sphere is suspended by means of an electric field between at least one pair of parallel charged plates. By controlling the magnitude of the electric charge on the parallel plates, the direction and magnitude of the electric field between the plates can be varied. This, in turn, modifies the force exerted on the charged sphere. Thus, by appropriately controlling the charge on the parallel plates, the position and movement of the sphere between the plates can be controlled.
The concept of actuators which use electric and/or magnetic fields to directly control the position and movement of an object appears quite promising. In terms of speed, grace, and efficiency, their performance can far exceed that of conventional actuators. Nevertheless, such actuators which have heretofore been constructed suffer from a number of significant disadvantages.
In order to create the required electric and/or magnetic fields to position an object in space, prior art actuators typically require a complex physical structure having component parts which require careful adjustment. For example, if an object is to be suspended by an electric field, some type of structure is typically required to support two parallel plates between which the object will be positioned. If movement in more than one dimension is desired, additional sets of parallel plates are provided, and such plates also require a suitable support structure. Significantly, the orientation of each set of plates must generally be fixed and adjusted quite carefully so that the position and movement of the object between the plates can be accurately controlled.
The physical support structure which is generally required for the prior art electric and magnetic field actuators results in such actuators being quite difficult, time consuming, and expensive to manufacture. In addition, due in part to the structural complexity of such actuators, it is difficult to make the actuators on a small scale. Thus, while the performance of the prior art electric and magnetic field actuators is an improvement over conventional actuators, such actuators are still relatively large and expensive.